1. Field of the Invention
The present invention relates to a fluorescence light detection device and a fluorescence light detection method configured to irradiate a test object with excitation light and detect fluorescence light produced by the test object.
2. Description of the Related Art
A growing number of fluorescence light detection devices have been used in the field of life science. A fluorescence light detection device is easy-to-use and has high detection sensitivity. A fluorescence light detection device may sometimes be used in combination with an amplification step for efficient quantitative detection of nucleic acid such as DNA marked by a fluorescent chemical substance.
For example, patent document 1 discloses a device including a light projection fiber for guiding excitation light onto a sample, a light receiving fiber for guiding fluorescence light produced by the sample, and a support means for supporting an emitting end of the light projection fiber and an incident end of the light receiving fiber.    [Patent document 1] JP2009-14379
However, a fluorescence light detection device in which a fiber for guiding excitation light and a fiber for guiding fluorescence light are provided as separate components as in patent document 1 has the following problem.
FIGS. 1A and 1B illustrate a problem with a fluorescence light detection device in which a fiber for guiding excitation light and a fiber for guiding fluorescence light are provided as separate components. FIG. 1A illustrates how excitation light emitted from an excitation light fiber 101 is focused by an objective lens 103 onto a sample S. FIG. 1B illustrates how fluorescence light emitted from a fluorescence light fiber 102 is focused by the objective lens 103 onto the sample S. In reality, the fluorescence light is produced in the sample S and travels toward the fluorescence light fiber 102 via the objective lens 103. For ease of understanding, the fluorescence light is considered as traveling in the opposite direction.
As shown in FIGS. 1A and 1B, given that the excitation light fiber 101 and the fluorescence light fiber 102 are provided as separate components, the image of the core end surface of the excitation light fiber 101 formed by the objective lens 103 on the sample S (hereinafter, referred to as “excitation light spot”) does not coincide with the image of the core end surface of the fluorescence light fiber 102 formed by the objective lens 103 on the sample S (hereinafter, referred to as “fluorescence light spot”). The images are displaced from each other. For example, it is assumed that the excitation light spot is formed at point A and the fluorescence light spot is formed at point B in the configuration of FIGS. 1A and 1B. Since the intensity of excitation light is at maximum at the excitation light spot A, the intensity of fluorescence light produced by the sample S is also at maximum at the excitation light spot A. However, the fluorescence light produced at the excitation light spot A is not captured by the fluorescence light fiber 102. The principle of reversibility of light path tells that the light produced at the fluorescence light spot B is captured by the fluorescence light fiber 102 at the maximum solid angle. Since the fluorescence light spot B is not irradiated by the excitation light, however, fluorescence light is not produced at the fluorescence light spot B in the first place. In this case, the distance between the objective lens 103 and the sample S need be adjusted so as to capture fluorescence light in a portion outside the excitation light spot or the fluorescence light spot in which the beams overlap. For example, the sample S may be brought closer to the objective lens 103 from where it is in FIGS. 1A and 1B. In other words, a defocused state need be induced. Naturally, however, fluorescence light cannot be captured at a high efficiency in a defocused state.
Thus, given that the excitation light fiber 101 and the fluorescence light fiber 102 are provided as separate components, the excitation light spot A having rich potential of producing an intense fluorescent signal and the fluorescence light spot B from which the fluorescence light fiber 102 can capture produced fluorescence light most effectively do not coincide at all so that it is difficult to detect fluorescence light of high intensity. Patent document 1 does not explicitly teach an objective lens but similarly indicates existence of misalignment between a region irradiated by excitation light and a region from which fluorescence light can be captured.